1. Field of the Invention
This invention relates to skin care compositions, and in particular, to improved skin care compositions for enhancing skin hydration and for providing excellent moisturizing, conditioning, and cosmetically acceptable tactile properties to the skin.
2. Background of the Related Art
Consumers have long desired hand and body lotions or creams which, when applied to the skin, provide cosmetically acceptable tactile properties. In response to this desire, lotions and creams have been formulated through the years to exhibit satisfactory feel, lubricity, and absorption upon application to the skin.
More recently, consumers have been introduced to specialty lotions and creams formulated to treat dry skin conditions. These specialty lotions and creams hereafter will be referred to as "dry skin formulations."
A particular dry skin formulation is set forth in U.S. Pat. No. 4,389,418 (the '418 patent), which is commonly assigned to the assignee of this application. The '418 patent is hereby incorporated by reference in its entirety.
The dry skin formulation of the '418 patent employs petrolatum or mineral oil as an occlusive agent, and glycerin as a humectant, in combination with a unique di-lower alkyl di-higher alkyl ammonium emulsifier, a fatty alcohol stabilizer, and a fatty ester emollient. As used herein, "occlusive agent" refers to any substance that physically prevents or reduces moisture loss from the skin by formation of a water-impenetrable barrier over the stratum comeum; "humectant" refers to any substance that chemically attracts and holds water to the outside surface and upper layers of the stratum comeum; "stratum corneum" refers to the outer exposed layer of the epidermis.
The dry skin formulation of the '418 patent exhibits excellent moisturizing and conditioning ability upon application to the skin. As used herein, "moisturizing ability" means the ability to increase the water content of the skin, and "conditioning ability" means the ability to improve consumer perception of skin softness and smoothness.
Our invention is directed to improving the moisturizing ability of the dry skin formulation of the '418 patent. We have discovered that increasing the amount of glycerin in this formulation and adding a small amount of plant-derived oil, both within specific ranges of weight percentages or weight ratios, results in an improved cosmetic formulation that synergistically and unexpectedly provides superior short-term skin hydration. As used herein, "skin hydration" refers to the relative water level present in the stratum corneum, as measured by an analytical instrument, such as a Nova DPM dermal phase meter; "short-term skin hydration" refers to the level of skin hydration effected between about 1 and about 12 hours after application of a formulation.
The cosmetics industry has long recognized vegetable (or plant-derived) oils as occlusive agents for reducing transepidermal water loss (hereafter "TEWL"). Recently, vegetable oils have gained popularity, due to the recognition that they provide other usefull cosmetic properties. However, prior to this invention, plant-derived oils had not been recognized for their significant ability to effect short-term skin hydration.
For example, U.S. Pat. No. 5,690,947 (hereafter "the '947 patent") discloses the use of borage seed oil in cosmetic compositions containing hydroxy acids and/or retinoids. The '947 patent only teaches the use of borage seed oil as an anti-irritant to ameliorate skin irritations commonly associated with the use of hydroxy acids and retinoids. This patent does not suggest using borage seed oil to enhance short-term skin hydration.
U.S. Pat. No. 5,620,692 (hereafter "the '692 patent") discloses the use of oat oil in cosmetic compositions to provide beneficial dermatological properties, such as UV-inhibition and anti-oxidancy, in addition to TEWL reduction. The '692 patent, though, does not suggest using oat oil to promote short-term skin hydration.
U.S. Pat. No. 4,375,480 (hereafter "the '480 patent") discloses a hypoallergenic facial skin emulsion having 8-35 parts by weight unsaturated vegetable oil. The vegetable oil serves as an emollient and a moisturizer, and most preferably is sesame oil. Unlike the present invention, the '480 patent does not suggest using vegetable oil to increase short-term skin hydration. Further, the '480 patent requires flushing the skin with water for 2 to 3 minutes immediately after application of the emulsion, in order to effect water absorption into the skin via the emulsion.
U.S. Pat. No. 5,656,278 (hereafter "the '278 patent") discloses dermatological and cosmetic compositions for restoring the barrier function of the stratum corneum. The compositions of this patent require the combination of at least one ceramide, as disclosed therein, and linoleic acid, to effect barrier function restoration. The linoleic acid is preferably obtained from vegetable oils rich in this fatty acid. However, the '278 patent does not disclose or suggest the use of linoleic acid, either alone or in combination with humectants, to improve short-term skin hydration.
U.S. Pat. No. 5,643,899 (hereafter "the '899 patent") discloses various lipid combinations useful for effecting epidermal moisturization and for repairing the barrier function of the stratum corneum. Some of the combinations include essential fatty acids, such as linoleic acid, as a component. Vegetable oils containing the required essential fatty acids may be used in the lipid combinations. Unlike the present invention, the '899 patent requires all of the lipids set forth therein, including vegetable oils, to be used in combination with at least one other non-vegetable-derived lipid. Moreover, the '899 patent does not disclose or suggest using vegetable oil to provide enhanced short-term skin hydration.
U.S. Pat. No. 4,740,367 (hereafter "the '367 patent") discloses the use of a vegetable oil adduct, produced by the Diels-Alder reaction with fumaric, maleic anhydride or acrylic aid, or a combination of the vegetable oil adduct and its parent vegetable oil, as an emollient/moisturizer in skin and hair compositions. The '367 patent suggests, as a preferred combination, soybean oil-fumaric acid adduct and soybean oil. However, the '367 patent does not disclose or suggest the use of vegetable oil, either alone or in combination with other humectants, to enhance short-term slin hydration.
U.S. Pat. No. 5,229,130 (hereafter "the '130 patent") relates to methods and compositions for enhancing skin permeation of pharmaceutically active agents across the stratum comeum. The skin permeation enhancing component is a vegetable oil, which preferably does not contain large amounts of saturated fatty acids or fatty acids having less than 8 or greater than 14 carbon atoms. The '130 patent prefers a combination of coconut and soybean oils. The '130 patent, however, does not disclose or suggest the utility of vegetable oils for enhancing skin permeation of water.
U.S. Pat. No. 4,632,772 (hereafter "the '772 patent") discloses an anti-microbial detergent composition having 2.2 to 14 parts by weight moisturizer/emollient as a component. The moisturizer/emollient may comprise a vegetable oil. Unlike the present invention, the moisturizer/emollient of the '772 patent functions to replace the natural skin oils which are lost or partially removed by the detergent composition. The '772 patent does not disclose or suggest using vegetable oil to provide enhanced short-term skin hydration.